Device for drawing parallel strips with uniform tension

ABSTRACT

A wide web of heat-sealable plastic material, continuously unwound from a supply roll, is slitted longitudinally into a plurality of parallel strips which are entrained by a motordriven traction roller and are allowed to hang in slack loops about one or more horizontal bars carried on the free end of a sensing lever, being then fed past an intermittently operating clamp and a drawing mechanism to an output stage where they pass through a set of friction rollers or rods and are periodically pulled forth for shaping into envelopes sealed about materials discharged from respective dispensers. With the drawing mechanism intermittently picking up the slack of the loops, the length of the shortest loop controls the position of the sensing lever which, on swinging beyond an upper or a lower limit, coacts with one of two stops to accelerate or retard the drive motor, thereby maintaining a proper average feed rate.

United States Patent Roussel s] 3,656,386 [4 1 Apr. 18, 1972 DEVICE FOR DRAWING PARALLEL STRIPS WITH UNIFORM TENSION Inventor:

Assignee:

Jean-Charles Roussel, Rhone, France Rhone, France Filed: July 17, 1970 Appl. No 55,764

Field of Search ..'..53/389; 83/367, 236, 209, 255, 83/277, 408, 72-74 References Cited UNITED STATES PATENTS 9/1963 Schoenberger, Jr. ..S3/236'X Societe Anonyme Thimonnler & Cle,

3,461,757 8/l 969 Healyetal. ..83/367X Primary Examiner-James M. Meister Attorney-Karl F. Ross [5 7] ABSTRACT A wide web of heat-scalable plastic material. continuously unwound from a supply roll, is slitted longitudinally into a plurality of parallel strips which are entrained by a motor-driven traction roller and are allowed to hang in slack loops about one or more horizontal bars carried on the free end of a sensing lever, being then fed past an intermittently operating clamp and a drawing mechanism to an output stage where they pass through a set of friction rollers or rods and are periodically pulled forth for shaping into envelopes sealed about materials discharged from respective dispensers. With the drawing mechanism intermittently picking up the slack of the loops, the length of the shortest loop controls the position of the sensing lever which, on swinging beyond an upper or a lower limit, coacts with one of two stops to accelerate or retard the drive motor, thereby maintaining a proper average feed rate.

10 Claims, 3 Drawing Figures HER/ED PATENTEmPR 18 I912 3,656,386

' SHEEIIUF 2 HEATED Jame-mans ROUSSEL INVENTOR ATTORNEY DEVICE FORDRAWING PARALLEL STRIPS WIT UNIFORM TENSION My present invention relates to a system for the drawing of a plurality of parallel strips, cut from a single web, to a load where these strips may be individually utilized for various purposes such as the packaging of goods issuing from a corresponding number of dispensers or spouts.

Packaging machines of this description may operate on pairs of intermittently advancing strips of heat-sealable plastic material, e.g. polyethylene foil, which can be thermally fused along their longitudinal and transverse edges to form envelopes around, say, a flowable substance discharged from a pipe bracketed by the strips. In order to ensure the accurate dosing of measured quantities of the substance to be dispensed, the strips concurrently payed out by the feed mechanism should be under substantially the same tension which theoretically is easy enough to-realize with the strips drawn from a web of uniform thickness. In practice, however, such uniformity is frequently lacking sothat the strips sliced from the web are not engaged with exactly the same pressure by a common traction roller or the like whereby the feed rate will differ among the several strips. Some of the strips, therefore, will be relatively taut while others are relatively slack when the entire array is engaged by theterminal stage of the feed mechanism, eg by abank of reciprocating grippers.

These difficulties apply both to individually gripped strips and to strips that are stacked when engaged by the feed mechanism. The problem is particularly complex, however, with packaging machines of the above-described type in which two sets of strips move in unison to form envelopes or bags.

The general object of my present invention, therefore, is to provide improved means for drawing such parallel strips with uniform tension from ,a common web of sheet material, notably but not exclusively for use with packaging machines of the type referred to.

A related object is to provide means in such a system for maintaining at the supply end an average delivery rate consistent with the rate of continuous or intermittent advance of the strips at the output end.

These objects are realized, pursuant to the present invention, by the provision of guide means for a plurality of strips sliced in conventional manner from a wider web, the guide means allowing the several strips to hang in slack loops beyond a traction roller or equivalent means for continuously drawing the sheet from a supply roll. Within these loops I position one or more feeler elements, e.g., bars or rollers, mounted horizontally on a movable carrier such as a lever for positive engagement by the shortest loop so as to occupy different positions upon variations in the length of that loop. The speed of the traction means is variable by a controller which responds to the movement of the feeler or feelers to maintain the proper delivery rate for the strips payed out downstream of the loop-forming guide means.

In an advantageous embodiment, the controller includes a pair of abutments which are respectively engageable by the feeler-carrying sensing lever in an upper and a lower terminal position of its swing. These abutments act, e.g. through a common link maintaining a constant spacing therebetween, upon a potentiometer or other circuit element adapted to vary the energization of a d-c motor or other prime mover for the traction drive.

If the advance of the strips at the output end is intermittent rather than continuous, the lever will swing in the rhythm of this advance over an are which normally should not cause any change in the speed of the traction drive. The abutments of the controller, therefore, will be engaged only when the lever swings beyond either the upper or the lower limit of its normal ran e.

A ccording to another feature of this invention, an intermittently operable clamp is disposed between the loop-forming guide means and the feed mechanism for the individual strips, this clamp releasing the strips whenever a drawing member just ahead of a frictional retaining device pulls a fresh length of strip from each loop; thislength is preferably somewhat greater than that needed to feed the load during the ensuing advance of the forwardends of the strips. The drawing member may be coupled with the load-side grippers for alternately tensioning and slackening the strips upstream and downstream of the retaining means which may be constituted by a set of friction rods or rollers.

The above and other features of my invention will be described in greater detail with reference to the accompanying drawing in which:

FIG. 1 is a somewhat diagrammatic side-elevational view of a system embodying the invention;

FIG. 2 is a view similar to FIG. 1, showing part of the system on a larger scale; and

FIG. 3 is a cross-sectional view taken on the line III III of FIG. 2.

In FIG. 1 there can be seen a pipe I which forms part of a bank of such pipes serving as dispensers for a flowable mass to be filled into sealed bags. The machinery associated with the pipes 1 includes a pair of heated jaws 4 which open and close horizontally and, when open, allow for the descent of a pair of parallel strips 2a, 2b alongside the pipe 1, the strips projecting laterally beyond the pipe so that their confronting longitudinal edges can be heat-sealed to each other upon contact with the closing jaws 4. The strips 2a, 2b (and corresponding strips moving parallel thereto along the other dispensing pipes) are intermittently pulled down, as indicated by an arrow 6, by a gripping mechanism comprising a pair of jaws 5 which are.

both horizontally separable and vertically reciprocable, their upper and lower limiting positions being shown in full and dotdash lines, respectively.

As is well known per se, gripper jaws 5 close in their elevated position about the sleeve formed from the marginally fused lower ends of strips 2a and 2b to pull that sleeve down across the open end of pipe 1, filling it with the material dispensed by that pipe and letting part of it pass between two further heated jaws 7 which are horizontally movable to form a transverse heat seal. A cutter, not shown, severs the sleeve midway through its transverse zone of fusion whereby the top of the bag thus made and the bottom of the remaining tubing are sealed preparatorily to a repetition of the cycle.

The strips 2a and 2b, which may consist of thermoplastic sheet material such as polyethylene, are cut from respective webs 3a, 3b of this material taken from a pair of substantially wider rolls A and B, respectively. Other strips drawn from the same two rolls have been indicated at 2a, 2"a and 2'b, 2"b, respectively. As the means for slitting the webs, guiding the resulting strips and feeding them to the machine 4 7 are identical for the two rolls A and B, only the mechanism associated with roll A will be described in detail; the same reference numerals, supplemented by a prime mark, are used to designate corresponding elements of the mechanism serving the roll B.

The web 3a, coming from the roll A, is successively wound around three larger deflecting rollers 13, 14, 15 and two smaller rollers 16, 17, passing finally about another larger roller 28 beyond which it is longitudinally slitted by a set of parallel, identically shaped blades 33 (only one shown). The resulting strips 2a, 2a', 2"a etc. are entrained by a traction roller 29 which is driven by an electric motor 32 and cooperates with a counterroller 30, thereby drawing these strips into loops which are allowed to hang slack into an upwardly open protective housing 44.

In order to prevent entanglement or crossovers between adjacent strips, it is advantageous to guide them over different paths whose length need not be identical since only the rate of advance of the strips along these paths determines the tension to which they are subjected when engaged by the respective gripper jaws 5. Thus, I have shown a series of guide rods 45, 46, 48, 49, 149, 55 and 155, most of these rods (which could also be rollers) occurring in pairs for the guidance of the oddnumbered and the even-numbered strips, respectively. The loops of the odd-numbered strips, such as the strip 20, em-

brace a feeler 36 whereas the loops of the even-numbered strips pass around another feeler 37; feelers 36 and 37 are a pair of horizontal bars which span two parallel levers 34 (seen respectively in FIGS. 1 and 2) bracketing the path of the web 3a. These bars are spaced sufficiently far apart to minimize their retarding effect upon the advance of the strips which therefore hang virtually unstressed into the housing 44.

For the reason stated at the outset, some loops will generally be longer than others while their relative lengths are subject to changes as the web 3a is progressively unwound from its supply roll A. In FIG. 1, for example, the loop of strip 2a is shown to be shorter than all the others so as to engage the feeler bar 36 whereby the free right-hand end of lever 34, whose opposite end is fixedly fulcrumed on a shaft 35, is held elevated against the force of gravity; in FIG. 2, strip 2a has the shortest loop which engages the bar 37 to hold the lever in its illustrated position. It will be apparent that the strips cooperating with the lower bar 37 may also pass around the upper bar 36 but that the strips designed to engage the bar 36 must bypass the bar 37.

Bars 36, 37 and levers 34 form part of a sensing device which determines the amount of slack in the shortest strip and generate signals for controlling the speed of drive motor 32 whenever this slack goes beyond either limit of a predetermined range. This variation in motor speed is achieved by a controller, best shown in FIG. 2, which comprises a pair of abutments 39, 40 above and below a ledge 38 on one of the levers 34. Abutments 39 are interconnected by a flexible but inextensible link diagrammatically illustrated as an endless belt or chain 41 passing around two pullies or sprocket wheels I42, 242, the latter wheel entraining the wiper 42 of a potentiometer 142 connected in the energizing circuit of motor 32. When the shortest loop has less than the desired minimum length, ledge 38 engages the upper strop 39 to turn the wiper 42 in a sense accelerating the motor 32 whereby the web 3a is drawn at a faster rate from its roll A. Conversely, an excessive lengthening of all the loops allows the lever 34 to drop under its own weight (possibly assisted by a spring) whereby the lower stop 40 is placed to turn the wiper in the opposite sense, with corresponding reduction in motor speed.

The intermittently operating feed system shown in FIG. 1 causes an alternate stretching and slackening of the strips whereby the lever 34 oscillates about its fulcrum 35, in the rhythm of the reciprocating grippers as long as the delivery rate of traction roller 29 matches the average feedout velocity of the strips, no change in motor speed is desired and the ledge 38 remains clear of the stops 39 and 40 which are sufficiently spaced apart for this purpose.

After passing around deflecting rods 45, the strips are engaged by the rods 46 which are vertically movable on the piston rod of a hydraulically, pneumatically or electromagnetically operated servomotor 47 synchronized with the grippers 5. Rods 46 coact with stationary plates 57 (FIG. 2) against which they clamp the strips when in their lowered position. This clamping action coincides with the descent of the grippers 5, the resulting stretching of the strips between these grippers and the clamps 46, 57 being facilitated by a corresponding rise of rod 49 which is mounted on the upper end of a movable arm 50 articulated to the free end of a lever 52 fixedly fulcrumed at 58. The lower end of arm 50 is articulated to a two-armed lever which pivots about a fulcrum 59 on the machine frame 12 under the control of a double-acting jack 11 whose fluid-operated plunger 111 is connected via a linkage 9 with one end of lever 10, the other end of that lever being connected with grippers 5 by way of a linkage 8. Thus, the periodic reciprocations of plunger lll lowers the grippers 5 while raising the arm 50, and vice versa, with rod 49 descending in the released state of clamps 46, 57 to draw a fresh supply of strip material from the loops in housing 44. The relative strokes of grippers 5 and pull rod 49 are so dimensioned that the reserve length drawn by that rod during a normal operating cycle is less than that payed out by the traction roller during such cycle (in order to prevent the complete flattening of any loop) but slightly exceeds the length drawn by the grippers.

In order to keep the strips taut around the dispensing pipes or spouts l, frictional retaining means in the form of rods and/or rollers 53, 53 engage them just before they reach the final vertical stretch of their path. The friction of these retaining elements is sufficient to prevent the rod 49 from exerting any appreciable stress upon the tenninal portions of the strips which are engaged by the heated jaws 4 when, with clamps 46, 57 open, the arm 50 descends so as to lower the rod 49. When the lever 10 has reached the end of its counterclockwise swing, the elevated gripper jaws 5 close while the clamps 46, 57 open and the grippers move downwardly (arrow 6); lever 10 now rotates clockwise (arrow 56) and the rod 49 rises to supply the material needed by the load, i.e. by the packaging machine partly illustrated at 4 7.

If the strips were fed continuously rather than intermittently to the load, e. g. with the aid of traction rollers taking the place of retaining means 53, 53, clamps 46, 57 and pull rod 49 could be omitted. In that case, of course, the abutments 39 and 40 could be moved much closer together since the lever 34 would swing only if the delivery rate and the motor speed did not keep pace with each other, taking into account any slippage at the traction roller and any elongation undergone by the strips between the cutters 33 and the load.

Means may be provided for continuously monitoring the alignment of the web 3a and the cutting blades 33 in order to keep the width of the strips as constant as possible and to prevent waste. Such a monitoring device, best illustrated in FIG. 3, comprises a pair of photocells 18 which flank the roller 16 and are normally illuminated by respective lamps 19 whose beams pass close to the lateral edges of the web 3a. Deflecting roller 15 is tiltably mounted in bearings 24 which can be raised and lowered by means of respective servomotors 23, similar to the one shown at 47, in response to the outputs of the two photocells as applied to respective control circuits 22. Bearings 24 receive the gudgeons 25 of roller 15 with sufficient play to let this roller assume an inclined position, exaggeratedly indicated by a dot-dash outline 21, by a rising of one or the other bearing, i.e. the bearing whose photocell 18 detects an excursion of the web from its normal path (e.g. to the left, arrow 26) which cuts off the light from the associated lamp 19. The compensatory tilting (clockwise) of roller 15, preceding the roller 16 in the direction of web motion, then recenters the web 3a on the roller 16 and therefore restores its alignment with blades 33.

Naturally, the system herein disclosed could also be used to control the advance of strips cut from a single web, rather than from two co-ordinated webs as shown in FIG. 1.

Like the lever 34, other elements (e.g. servomotor 47 and arm 50) may also be symmetrically duplicated on opposite sides of the strip path for a balanced mounting of the guide means straddling this path.

Iclaim:

1. A system for feeding a plurality of of parallel strips of flexible sheet material with equal tension to a load, comprismg:

supply means for delivering a wide web of said sheet materitraction means for continuously drawing said web from said supply means;

cutter means adjacent said traction means for slitting said sheet into parallel strips;

guide means for said strips allowing same to hang in slack loops beyond said traction means;

feed means beyond said guide means for concurrently advancing said strips to the load;

feeler means embraced by all said loops for positive engagement by the shortest loop to occupy different positions upon variations in the length of said shortest loop;

and control means actuatable by said feeler means for varying the speed of said traction means to maintain an average delivery rate consistent with the rate of advance of the strips by said feed means.

2. A system as defined in claim 1 wherein said control means comprises a vertically movable sensing member carrying said feeler means and a pair of abutments respectively engageable by said member in an upper and a lower terminal position thereof.

3. A system as defined in claim 2 wherein said control means further comprises a movable link carrying said abutments with constant relative spacing.

4. A system as defined in claim 3 wherein said member is a lever, said feed means being intermittently operative to advance said strips whereby said lever oscillates in the rhythm of the strip movement, the spacing of said abutments being greater than the oscillating stroke of said lever due to said movement.

5. A system as defined in claim 4 wherein said feed means comprises frictional retaining means for said strips ahead of the load and reciprocating drawing means ahead of said retaining means for pulling a length of each strip less than that stored in the respective loop.

6. A system as defined in claim 5, further comprising intermittently operable clamping means for said strips synchronized with said feed means to release said strips during a pulling stroke of said drawing means.

7. A system as defined in claim 5 wherein said feed means further comprises gripper means beyond said retaining means intermittently engageable with said strips for pulling same through said retaining means, said gripper means and said drawing means being provided with a synchronizing linkage for the alternate tensioning and slackening of the strips upstream and downstream of said retaining means.

8. A system as defined in claim 1 wherein said cutter means comprises a set of blades ahead of said traction means, further including monitoring means for maintaining a predetermined alignment between said blades and said web.

9. A system'as defined in claim 8 wherein said monitoring means comprises a pair of photoelectric devices disposed at opposite edges of said web for detecting deviations thereof from a predetermined path, and adjustment means responsive to said devices for redirecting the web onto said path in the presence of such deviations.

10. A system as defined in claim 9 wherein said adjustment means comprises a guide roller for said web and mounting means for limitedly inclining said guide roller at different angles with reference to said path. 

1. A system for feeding a plurality of of parallel strips of flexible sheet material with equal tension to a load, comprising: supply means for delivering a wide web of said sheet material; traction means for continuously drawing said web from said supply means; cutter means adjacent said traction means for slitting said sheet into parallel strips; guide means for said strips allowing same to hang in slack loops beyond said traction means; feed means beyond said guide means for concurrently advancing said strips to the load; feeler means embraced by all said loops for positive engagement by the shortest loop to occupy different positions upon variations in the length of said shortest loop; and control means actuatable by said feeler means for varying the speed of said traction means to maintain an average delivery rate consistent with the rate of advance of the strips by said feed means.
 2. A system as defined in claim 1 wherein said control means comprises a vertically movable sensing member carrying said feeler means and a pair of abutments respectively engageable by said member in an upper and a lower terminal position thereof.
 3. A system as defined in claim 2 wherein said control means further comprises a movable link carrying said abutments with constant relative spacing.
 4. A system as defined in claim 3 wherein said member is a lever, said feed means being intermittently operative to advance said strips whereby said lever oscillates in the rhythm of the strip movement, the spacing of said abutments being greater than the oscillating stroke of said lever due to said movement.
 5. A system as defined in claim 4 wherein said feed means comprises frictional retaining means for said strips ahead of the load and reciprocating drawing means ahead of said retaining means for pulling a length of each strip less than that stored in the respective loop.
 6. A system as defined in claim 5, further comprising intermittently operable clamping means for said strips synchronized with said feed means to release said strips during a pulling stroke of said drawing means.
 7. A system as defined in claim 5 wherein said feed means further comprises gripper means beyond said retaining means intermittently engageable with said strips for pulling same through said retaining means, said gripper means and said drawing means being provided with a synchronizing linkage for the alternate tensioning and slackening of the strips upstream and downstream of said retaining means.
 8. A system as defined in claim 1 wherein said cutter means comprises a set of bladeS ahead of said traction means, further including monitoring means for maintaining a predetermined alignment between said blades and said web.
 9. A system as defined in claim 8 wherein said monitoring means comprises a pair of photoelectric devices disposed at opposite edges of said web for detecting deviations thereof from a predetermined path, and adjustment means responsive to said devices for redirecting the web onto said path in the presence of such deviations.
 10. A system as defined in claim 9 wherein said adjustment means comprises a guide roller for said web and mounting means for limitedly inclining said guide roller at different angles with reference to said path. 